CN104979852B

CN104979852B - Power distribution system

Info

Publication number: CN104979852B
Application number: CN201510169219.9A
Authority: CN
Inventors: E.路易斯
Original assignee: GE Energy Power Conversion Technology Ltd
Current assignee: GE Energy Power Conversion Technology Ltd
Priority date: 2014-04-10
Filing date: 2015-04-10
Publication date: 2020-02-07
Anticipated expiration: 2035-04-10
Also published as: EP2930815A1; US10020652B2; BR102015007967B1; BR102015007967A2; CA2887084A1; US20150295403A1; CN104979852A; EP2930815B1; ES2706420T3

Abstract

The invention discloses a power distribution system. The system includes a first AC bus and a second AC bus connected to an AC generator. A first active rectifier/inverter has AC input terminals electrically connected to the first AC bus. A second active rectifier/inverter has AC input terminals electrically connected to the second AC bus. A first DC interface is electrically connected to the DC output terminals of the first active rectifier/inverter and a second DC interface is electrically connected to the DC output terminals of the second active rectifier/inverter. The first DC interface and the second DC interface comprise reverse blocking means. A third active rectifier/inverter operates as a driver and has DC input terminals electrically connected in parallel to the DC output terminals of the first and second DC interfaces by a plug-in DC bus. An electric motor, which may optionally form part of marine propulsor T1, is electrically connected to the AC output terminals of the third active rectifier/inverter.

Description

Power distribution system

Technical Field

The present invention relates to power distribution systems, and more particularly to marine power distribution and propulsion systems. The term "marine vessel" is intended to include ships, drilling rigs, and any other surface-traveling vessel or platform, or submersible (underwater) vessels.

Background

Marine power distribution and propulsion systems are well known. In a typical arrangement, a series of power converters are used to couple a direct current (AC) bus to a series of electric motors, such as propulsion motors or propellers. Each power converter may be an "active front end" (AFE) converter with an AC mains-side active rectifier/inverter (or "front end" bridge) having AC terminals connected to the AC bus and a motor-side active rectifier/inverter connected to the motor. The alternating current (DC) output of the AC mains-side active rectifier/inverter is connected to the DC input of the motor-side active rectifier/inverter by a DC link. A harmonic filter may be connected to the AC input terminals of each AC mains-side rectifier/inverter. In normal operation, the AC mains-side rectifier/inverter will operate as an active rectifier to supply power to the DC link, and the motor-side active rectifier/inverter will operate as an inverter to supply power to the motor. In some cases, reverse operation is generally possible, as for regenerative braking in the case where the motor operates as a generator and power is supplied to the AC bus through the power converter.

Each active rectifier/inverter will typically have a conventional topology.

In some arrangements, the electric motor may be coupled to the AC bus by a plurality of parallel power converters.

A series of prime movers (e.g., diesel engines) are connected to a separate generator that supplies power to the AC bus.

The AC bus may be equipped with protective switchgear with circuit breakers and associated controls.

A marine propulsion system will typically comprise a first (or port) AC bus and a second (or starboard) AC bus interconnected by a bus tie (busbartie). Some marine propulsion systems use multiple AC bus sections or groups interconnected by multiple bus ties to improve power availability.

Marine vessels sometimes operate using Dynamic Positioning (DP) systems in which propulsion motors and/or propellers are used to maintain the vessel position near a reference point and stabilize its heading against environmental forces such as wind and water currents. The guidelines for marine vessels with DP systems are set by a number of certification authorities, e.g. norwegian classification societies (DNV), and there are certain requirements on the number and location of propulsion motors and propellers (e.g. bow or stern) that must be operable during a fault condition. For example, in an arrangement with two propulsion motors and two or three bow thrusters (e.g. tunnel thrusters) located at the stern of a marine vessel, the guidelines, and particularly those on the DNV class designation DYNPOS AUTR, require that the marine vessel have one operable propulsion motor at the stern, and either one operable bow thruster (if the thrusters are rated the same as the operable propulsion motor at the stern) or two operable bow thrusters (if the combined rating of the thrusters is the same as the operable propulsion motor at the stern).

For a marine propulsion system using three bow thrusters, in order to comply with the DNV classification symbol DYNPOS-AUTR, one of the bow thrusters must be powered by two different AC bus sections of such a design: the design ensures that this bow thruster maintains power without any power outage even if total power losses occur on any of the AC bus sections to which this bow thruster is connected.

Disclosure of Invention

The present invention provides a power distribution system, comprising:

a. a first direct current (AC) bus;

b. a second AC bus;

c. a first active rectifier/inverter having: an AC input terminal electrically connected to the first AC bus, and a DC output terminal;

d. a second active rectifier/inverter having: an AC input terminal electrically connected to the second AC bus, and a DC output terminal;

e. a first alternating current (DC) interface including a reverse blocking device and having: a DC input terminal electrically connected to the DC output terminal of the first active rectifier/inverter, and a DC output terminal;

f. a second DC interface comprising a reverse blocking device and having: a DC input terminal electrically connected to the DC output terminal of the second active rectifier/inverter, and a DC output terminal;

g. a third active rectifier/inverter having: a DC input terminal electrically connectable in parallel to the DC output terminal of the first DC interface and the DC output terminal of the second DC interface, and an AC output terminal, optionally through a DC bus; and

h. a motor electrically connected to the AC output terminals of the third active rectifier/inverter.

It should be noted that the electrical connection between two or more components of the electrical distribution system need not be a direct connection, and the electrical connection may be made by, or include, a plug-in component.

The first and second DC interfaces may have any suitable configuration and function to maintain an electrical connection between the first and second active rectifier/inverters and the third active rectifier/inverter over a range of operating conditions.

Each DC interface may have any suitable reverse blocking device to provide automatic disconnection from the first or second active rectifier/inverter in the event that one of the first and second active rectifier/inverters is unable to supply power and to prevent propagation of a fault (e.g., a short circuit) between the first and second active rectifier/inverters. In one arrangement, each reverse blocking device may comprise one or more diodes, or other types of power semiconductors with suitable reverse voltage withstanding properties (e.g. thyristors with reverse blocking action, IGBTs, IGCTs, GTOs and IEGTs).

In one arrangement, each DC interface comprises a first DC circuit line between a first DC input terminal and a first DC output terminal and a second DC circuit line between a second DC input terminal and a second DC output terminal. If each reverse blocking device comprises a power semiconductor device, a first string of one or more series-connected power semiconductor devices may be positioned in each first DC circuit line, with each anode electrically connected to the first DC input terminal and each cathode electrically connected to the DC output terminal. A second string of one or more series connected power semiconductor devices may be positioned in each second DC circuit line with each anode electrically connected to a second DC output terminal and each cathode electrically connected to a second DC input terminal. Generally speaking, a first portion of each reverse blocking device may be positioned in each first DC circuit line to provide a reverse blocking action that allows power flow from the first DC input terminal to the first DC output terminal and prevents power flow from the first DC output terminal to the first DC input terminal, and a second portion of each reverse blocking device may be positioned in each second DC circuit line to provide a reverse blocking action that allows power flow from the second DC output terminal to the second DC input terminal and prevents power flow from the second DC input terminal to the second DC output terminal or vice versa. In other words, the first and second parts of each reverse blocking arrangement are adapted to prevent power flow in opposite directions through the first and second DC circuit lines of each DC interface. The first DC input terminal of the third active rectifier/inverter may be electrically connected to the first DC output terminal of the first DC interface and the first DC output terminal of the second DC interface, optionally through a DC bus. The second DC input terminal of the third active rectifier/inverter may be electrically connected to the second DC output terminal of the first DC interface and the second DC output terminal of the second DC interface, optionally through a DC bus.

A monitoring circuit may be provided for fault detection of the reverse blocking arrangement. For example, the monitoring circuit may be positioned above each power semiconductor device or one or more series-connected power electronic devices per string.

At suitable locations in each DC circuit line, i.e. between one of the DC input terminals and a respective one of the DC output terminals, each DC interface may also comprise one or more of the following components:

DC fuses, for example, to prevent short circuits on optional DC busses;

a circuit breaker;

a common mode inductor filter.

For normal operation, the circuit breakers in the first DC interface and the second DC interface must be closed so that the power loss in the first AC bus or the second AC bus does not result in a power loss of the motor. The circuit breaker may open when the power distribution system is to be operated using power from only one of the AC buses (i.e., through only one of the first and second active rectifier/inverters). This mode of operation is for abnormal conditions and does not comply with the DNV ship-level notation DYNPOS AUTR or similar requirements.

The common mode inductor filter may optionally have a damping resistor on the coupling winding. In other words, the common mode inductor filter may have a first winding electrically connected to the first DC circuit line of the DC interface, a second winding electrically connected to the second DC circuit line of the DC interface, and a coupling winding electrically connected to the damping resistor. Such a common mode inductor filter will allow current to flow when the DC currents in the DC circuit lines are substantially equal and opposite. However, if the DC current in the DC circuit lines is unbalanced, the common mode inductor filter will add significant impedance to limit the possible circulating current between the first and second active filter/inverters.

In one arrangement, the first active rectifier/inverter may be part of a first power converter for coupling the second electric motor to the first AC bus and/or the second active rectifier/inverter may be part of a second power converter for coupling the third electric motor to the second AC bus. Each power converter may be an "active front end" (AFE) converter. In particular, the first power converter may comprise a first active rectifier/inverter and a fourth active rectifier/inverter having: a DC input terminal electrically connected to the DC output terminal of the first active rectifier/inverter through a DC link in parallel with the DC input terminal of the first DC interface, and to the AC output terminal of the second electric motor.

The second power converter may include a second active rectifier/inverter and a fifth active rectifier/inverter having: a DC input terminal electrically connected to the DC output terminal of the second active rectifier/inverter through a DC link in parallel with the DC input terminal of the second DC interface, and to the AC output terminal of the third electric motor.

Thus, it will be readily appreciated that the first DC interface is electrically connected to the DC link between the active rectifier/inverters of the first power converter and/or the second DC interface is electrically connected to the DC link between the active rectifier/inverters of the second power converter.

The second electric motor may be electrically connected to the first AC bus by one or more additional power converters in parallel with the first power converter. Similarly, the third electric motor may be electrically connected to the second AC bus by one or more additional power converters in parallel with the second power converter. Each additional power converter may be an AFE converter as described in this specification. It is expected that operation of the second and/or third motor at substantially rated power will require all of the power converters in parallel. In some cases, for example when the second motor and/or the third motor are not operating at rated power, no additional power converter may be needed, such that the second motor may operate using only the first power converter and/or the third motor may operate using only the second power converter. In some other cases, the second motor and/or the third motor may be operated using only the additional power converter, such that the second motor may be separate from the first power converter and/or the third motor may be separate from the second power converter. One example may be where one or both of the first active power converter and the second active power converter are used to provide power to the first motor through a DC interface.

A contactor may be located between the first power converter and the second motor to selectively separate the first DC interface from a further power converter for the second motor. Similarly, a contactor may be located between the second power converter and the third motor to selectively separate the second DC interface from the additional power converter for the third motor.

For example, the active rectifier/inverter employed in the power distribution system may have any suitable topology, such as a two-level or three-level neutral point clamped topology or a multi-level topology with a series of semiconductor power switching devices (e.g., IGBTs, IGCTs, and IEGTs) that are fully controlled and regulated using a pulse width modulation strategy.

The first and second active rectifier/inverters may include one or more of a DC output capacitor, an AC side harmonic filter, and AC side contactors for pre-charging the DC output capacitor and starting and stopping the active rectifier/inverter.

The third active rectifier/inverter (and optionally the fourth and fifth active rectifier/inverters) may include one or both of a DC input capacitor and an AC side filter inductor.

In normal operation, the first and second active rectifier/inverters will operate as rectifiers and the third active rectifier/inverter will operate as an inverter, i.e. such that the direction of power flow is from the first and second AC buses to the first motor. During normal operation, power flow through each power converter (i.e., the first and second power converters and any additional power converters) used to couple the second and third motors to the AC bus coupling will be in the same direction. However, the direction of power flow through each power converter can also optionally be reversed, for example, during regenerative braking in which the second and/or third electric motors operate as generators to supply power to the AC bus. It is not possible to reverse the direction of power flow through the first and second DC interfaces due to the reverse blocking means providing a reverse blocking action. An optional dynamic braking unit may be provided as part of the power distribution system if it is desired for the first electric motor to operate as a generator. For example, such a dynamic braking unit may be connected to the DC input terminals of the third rectifier/inverter in a conventional manner.

The first AC bus and the second AC bus may have any suitable number of phases, but three phases will be typical.

A bus tie line may be used to selectively connect the first AC bus and the second AC bus together.

The first AC bus and the second AC bus may be divided into separate sections. All connections to the AC bus and between individual bus sections may include protective switchgear (e.g., circuit breakers), or other protection circuits for separation purposes.

At least one AC generator will typically be electrically connected to each of the first AC bus and the second AC bus. The AC generator provides AC power to an AC bus and has an associated prime mover (e.g., a turbine or a diesel engine). Any suitable number of AC generators may be provided. Each AC generator may have an associated voltage controller or regulator, such as an Automatic Voltage Regulator (AVR).

Each motor employed in the power distribution system may be of any suitable construction and type (i.e., induction, synchronous, permanent magnet, etc.) and have any suitable number of phases.

The power distribution system as described herein may be a marine power distribution and propulsion system. In this case, each motor may be used to drive a propeller, for example, a multi-bladed propeller or a ducted pump injector. For example, each electric motor may be located within the hull of the marine vessel (e.g., as an inboard propulsion motor that drives a propeller through an axis with a stern tube gland), suspended in a compartment beneath the hull of the marine vessel, or coaxially outside the hull of the submarine. Each electric motor may form part of a propulsion motor or a propeller such as a bow propeller or a stern propeller for providing the main propulsion force for the marine vessel.

It will be readily appreciated that a particular marine vessel may only have any suitable number and configuration of motors (and associated junction power converters) depending on its propulsion requirements.

The basic power distribution system may have different modes of operation.

For example, during a normal or non-fault condition, power may be supplied to the DC bus from the first and second AC buses through the first and second active rectifier/inverters and the first and second DC interfaces. In other words, the DC bus will receive power from both the first AC bus and the second AC bus.

The control system may be used to control the power flow through the first active rectifier/inverter and the second active rectifier/inverter. Typically, the power flow through the first active rectifier/inverter and the second active rectifier/inverter will be substantially the same, but the control system may also allocate different power flows depending on the situation. The control system may also be used to control the power flow through the third active rectifier/inverter to the first motor. For example, the active rectifier/inverter may be controlled to provide the required torque to maintain the first motor at the desired rotational speed.

During normal operation, the bus tie may be opened or closed. Opening the bus tie is typically used to achieve maximum power availability because it minimizes the impact due to a fault in one of the AC bus sections. The AC voltages carried by the first and second AC busses may have different magnitudes, phases, or frequencies if the buss tie lines are open, which is possible due to the operation of the first and second active rectifier/inverters.

If a fault occurs on one or more of the first AC bus, the first active rectifier/inverter, and the first DC interface, the first motor will automatically disconnect from the first AC bus by the reverse blocking action of the reverse blocking device in the first DC interface without opening the circuit breaker in the first DC interface, and the increased power will continue to flow from only the second AC bus to the DC bus. Similarly, if a fault occurs on one or more of the second AC bus, the second active rectifier/inverter, and the second DC interface, the first motor will automatically disconnect from the second AC bus by the reverse blocking action of the reverse blocking device in the second DC interface, and the increased power will continue to flow from only the first AC bus to the DC bus. The automatic disengagement of the first motor occurs without significant delay, for example due to the instantaneous reverse blocking action of the power semiconductor device or other reverse blocking device. Decoupling the first motor means that it can continue to operate during the fault condition.

The arrangement of the power distribution system including one or more additional motors and a junction power converter (e.g., the first motor and/or the second motor, and the AFE converter) may also have different operating modes.

For example, during normal or fault-free operation, if the first motor does not need to operate, the second motor and/or the third motor may operate in the usual manner using respective parallel AFE converters.

If it is desired to operate the first motor, the first DC interface may be decoupled from the second motor and/or the second DC interface may be decoupled from the third motor (e.g., by actuating each contactor) such that the second motor and/or the third motor only receives power through the additional power converter. In other words, the second motor will no longer receive power from the first power converter, and the third motor will no longer receive power from the second power converter. The first and second power converters will not normally be used to simultaneously supply electric power to both the second and third electric motors and the first electric motor. To operate the first motor, power may be supplied to the DC bus from the first and second AC buses through the first and second active rectifier/converters of the first and second power converters and the first and second DC interfaces. Operation of the first motor during normal and fault conditions is as described above.

In the case of a marine power distribution and propulsion system, the first motor may be a bow thruster that is not used for marine propulsion, but only for Dynamic Positioning (DP), when the marine vessel is moving at substantially fixed or low speeds. The second and third electric motors may be propulsion motors located at the stern of the marine vessel, and typically all available AFE converters will be used in order to reach maximum marine vessel speed, i.e. when the second and third electric motors are operating substantially at rated power.

The marine power distribution and propulsion system of the present invention may comply with the DYNPOS AUTR requirement if an additional bow thruster is connected to each of the first AC busbar and the second AC busbar, for example by engaging an AFE converter. For example, if there is a fault on the second AC bus 2b, the marine vessel will have one operable propulsion motor (i.e., the second propulsion motor PM1) and two operable bow thrusters (i.e., the bow thruster T1 that will receive power from the first AC bus through the first active rectifier/inverter and the first DC interface and the additional bow thruster connected to the first AC bus) at the stern. It will be readily appreciated that due to a fault on the second AC bus, the third motor and the further bow thruster connected to the second AC bus will be disabled.

Drawings

FIG. 1 is a schematic diagram showing a first vessel power distribution and propulsion system according to the present invention; and

fig. 2 is a schematic diagram showing a second marine power distribution and propulsion system according to the present invention.

Detailed Description

While the following description relates to a marine power distribution and propulsion system, it will be readily appreciated that the power distribution system of the present invention is not limited to marine applications.

A first arrangement of a marine power distribution and propulsion system according to the invention is shown in figure 1. The system comprises a first AC bus 2a and a second AC bus 2 b.

The AC generator G1 is electrically connected to an associated prime mover (e.g., a diesel engine, not shown) and supplies AC power to the first AC bus 2 a. The AC generator G2 is also electrically connected to an associated prime mover (e.g., a diesel engine, not shown) and supplies AC power to the second AC bus 2 b. The generators G1, G2 are electrically connected to respective AC buses through protective switchgear 4, or other switchgear, having circuit breakers and associated controls. It will be readily appreciated that the system may have any suitable number of AC generators and any suitable bus configuration depending on the power generation and distribution requirements.

The

AC busbars

2a, 2b are interconnected by a busbar 6.

The system includes an electric motor forming part of a propeller (e.g., bow propeller T1) coupled to the

AC bus

2a, 2 b.

The first active rectifier/inverter assembly 8a is electrically connected to the first AC bus 2a and the second active finisher/inverter assembly 8b is electrically connected to the second AC bus 2 b. The active rectifier/

inverter assemblies

8a, 8b are electrically connected to the respective

AC bus bars

2a, 2b through protective switchgear 10, or other switchgear, having circuit breakers and associated controls.

For example, each of the active rectifier/inverter assemblies includes an active rectifier/

inverter

12a, 12b, the active rectifier/

inverter

12a, 12b having any suitable topology, such as a two-level or three-level neutral point clamped topology or a multi-level topology having a series of semiconductor power switching devices (e.g., IGBTs, IGCTs, and IEGTs) that are fully controlled and regulated using a pulse width modulation strategy. The DC output terminals of each active rectifier/

inverter

12a, 12b are electrically connected to a

DC link

14a, 14b that includes a

DC output capacitor

16a, 16 b. The AC input terminals of each active rectifier/

inverter

12a, 12b are electrically connected to the

respective AC bus

2a, 2b through

contactors

18a, 18b, which contactors 18a, 18b can be actuated to pre-charge the

DC output capacitors

16a, 16b and can be actuated to start and stop the active rectifier/inverter. Each active rectifier/inverter assembly includes an AC side

harmonic filter

20a, 20 b.

The

DC link

14a, 14b of each active rectifier/

inverter assembly

8a, 8b is electrically connected to a respective

DC interface assembly

22a, 22 b.

Each

DC interface assembly

22a, 22b comprises a first DC circuit line between a first DC input terminal and a first DC output terminal, and a second DC circuit line between a second DC input terminal and a second DC output terminal. Each DC circuit line of the first DC interface assembly 22a includes a DC fuse 24a for preventing a short circuit on the DC bus 34, the circuit breaker 26a, the common mode inductor filter 28a, and the string of one or more series connected diodes 30 a. Similarly, each DC circuit line of the second DC interface assembly 22b includes a DC fuse 24b, a circuit breaker 26b, a common mode inductor filter 28b, and a string of one or more diodes 30b connected in series. The series connected

diodes

30a, 30b in each

DC interface assembly

22a, 22b cause the respective assembly to automatically disconnect from the first and second active rectifier/

inverter assemblies

8a, 8b if the first and second active rectifier/

inverter assemblies

8a, 8b are unable to supply power. The automatic disconnection occurs instantaneously and is a result of the reverse blocking action of the

diodes

30a, 30 b. The reverse blocking action of the

diodes

30a, 30b also prevents propagation of a fault (e.g., a short circuit) between the active rectifier/

inverter assemblies

8a, 8 b.

Each series connected

diode

30a, 30b is connected to a

monitoring circuit

32a, 32b for fault detection.

Each common

mode inductor filter

28a, 28b includes a damping resistor on the coupling winding (as shown in fig. 1) and adds significant impedance to limit possible circulating currents between the active rectifier/

inverter components

8a, 8 b.

The

DC interface assemblies

22a, 22b are connected in parallel to a common DC bus 34. Specifically, the DC bus 34 includes: a first DC circuit line connected to the first DC output terminal of each

DC interface component

22a, 22 b; and a second DC circuit line connected to the second DC output terminal of each DC interface component.

The third active rectifier/inverter assembly 36 includes an active rectifier/inverter 38, the active rectifier/inverter 38 operating as a motor drive and having DC input terminals electrically connected to the DC bus 34 and AC output terminals electrically connected to the motor of the bow thruster T1. For example, the active rectifier/inverter 38 may have any suitable topology, such as a two-level or three-level neutral point clamped topology or a multi-level topology having a series of semiconductor power switching devices (e.g., IGBTs, IGCTs, and IEGTs) that are fully controlled and regulated using a pulse width modulation strategy. The DC input terminals of the active rectifier/inverter 38 are electrically connected to a DC link 40 that includes a DC input capacitor 42.

The motor forming part of the bow thruster T1 may be of any suitable type and configuration.

During normal or non-fault conditions, power may be supplied to the DC bus 34 from the first and

second AC buses

2a and 2b through the first and second active rectifier/

inverter assemblies

8a and 8b and the first and second

DC interface assemblies

22a and 22 b. In other words, the DC bus 34 will receive power from both the first AC bus 2a and the second AC bus 2 b.

A control system (not shown) will control the power flow through the first and second active rectifier/

inverter assemblies

8a and 8 b. Typically, the power flow through the first and second active rectifier/

inverter assemblies

8a and 8b will be substantially the same, but the control system may also distribute different power flows depending on the circumstances. The control system may also be used to control the power flow to the motor through the active rectifier/inverter assembly 36. The various active rectifiers/inverters may be controlled to provide the required torque to maintain the motors at the desired rotational speed so that the bow thrusters T1 provide the desired thrust, for example for Dynamic Positioning (DP) of the marine vessel.

The busbar junction 6 may be opened or closed during normal operation, and will typically be open during a fault condition.

If a fault occurs on one or more of the first AC bus 2a, the first active rectifier/inverter assembly 8a and the first DC interface assembly 22a, the motor will be automatically isolated from the first AC bus by the instantaneous reverse blocking action of the series connected diodes 30a in the first DC interface assembly and the increased power will continue to flow only from the second AC bus to the DC bus 34 or vice versa. Thus, the bow thruster T1 will continue to operate during a fault condition using power supplied from the second AC bus 2b through the second active rectifier/inverter assembly 8b, the second DC interface assembly 22b and the DC bus 34.

A second arrangement of the marine power distribution and propulsion system according to the invention is shown in figure 2. The second arrangement is similar to the first arrangement and similar parts have been given the same reference signs. Where the individual components in fig. 2 are not given reference numerals, then they may be assumed to be the same as the corresponding components in the first arrangement shown in fig. 1, for example those components that form part of the first and second

DC interface assemblies

22a, 22b, the active rectifier assembly 36, and some of the AC supply side components of the first and second active rectifier/

inverter assemblies

8a, 8 b.

In a second arrangement, the first active rectifier/inverter assembly 8a forms part of a power converter 100c for coupling a further electric motor forming part of a first stern-mounted propulsion motor PM1 to the first AC bus 2 a. The second active rectifier/inverter assembly 8a forms part of a power converter 100d for coupling a further electric motor forming part of a second stern-mounted propulsion motor PM2 to the second AC bus 2 b.

The electric motor forming part of first propulsion motor PM1 is coupled to first AC bus 2a by three parallel-coupled

power converter assemblies

100a, 100b, and 100 c. Similarly, an electric motor forming part of second propulsion motor PM2 is coupled to second AC bus 2b by three parallel

power converter assemblies

100d, 100e, and 100 f. The power converter assemblies 100a-f are electrically connected to respective AC busses 2a, 2b through protective switchgear 102, or other switchgear, having circuit breakers and associated controls.

Each power converter assembly 100a-f includes an active rectifier/inverter assembly 104a-f that is identical to the active rectifier/

inverter assemblies

8a, 8b described above. Thus, it will be readily appreciated that each power converter assembly 100a-f is an "active front end" (AFE) converter. The DC output terminals of each active rectifier/inverter 106a-f are electrically connected to a DC link 108a-f that includes a DC output capacitor 110 a-f.

Each power converter assembly 100a-f also includes an active rectifier/inverter 112a-f, which active rectifier/inverter 112a-f operates as a motor drive and has DC input terminals electrically connected to the DC links 108a-f and AC output terminals electrically connected to the electric motor of the respective propulsion motor PM1, PM 2. Each DC link 108a-f includes a DC input capacitor 114 a-f. For example, the active rectifier/inverters 112a-f may have any suitable topology, such as a two-level or three-level neutral point clamped topology or a multi-level topology with a series of semiconductor power switching devices (e.g., IGBTs, IGCTs, and IEGTs) that are fully controlled and regulated using a pulse width modulation strategy.

The first DC interface assembly 22a and the active rectifier/inverter 112c for the power converter assembly 100c are both connected in parallel to the DC link 108 c. Similarly, the second DC interface assembly 22b and the active rectifier/inverter 112d for the power converter assembly 100d are both connected in parallel to the DC link 108 d.

Power converter assembly 100c is electrically connected to an electric motor forming a portion of first propulsion motor PM1 through contactor 116, and power converter assembly 100d is electrically connected to an electric motor forming a portion of second propulsion motor PM2 through contactor 118.

Although not shown in fig. 2, it will be readily appreciated that one or more additional electric motors (e.g., each forming part of a propeller or propulsion motor) may be coupled to the

AC bus bars

2a, 2b by one or more similar power converter assemblies.

During normal or no-fault operation, and if the bow thruster T1 is not required, the first propulsion motor PM1 and the second propulsion motor PM2 will receive power from the first AC bus 2a and the second AC bus 2b through the power converter assemblies 100a-f in the usual manner. The

contacts

116, 118 will close.

If the bow thruster T1 is required, for example for DP, the

contactors

116, 118 are opened and the electric motors forming part of the bow thruster will receive power from the first and

second AC buses

2a, 2b through the active rectifier/

inverter assemblies

104c, 104d of the

power converter assemblies

100c, 100 d. First and second propulsion motors PM1, PM2 may also operate, but not at full power rating, as they may still receive power from first and

second AC buses

2a, 2b through the remaining power converter assemblies. They will not receive power through the

power converter assemblies

100c, 100 d.

If a fault occurs on one or more of the first AC bus 2a, the power converter assemblies 100a-c and the first DC interface assembly 22a, the electric motor forming part of the bow thruster T1 may be disconnected from the first AC bus 2a by the momentary reverse blocking action of the series connected diodes 30a in the first DC interface assembly and the added power will continue to flow from the second AC bus 2b to the DC bus 34 or vice versa. Thus, the bow thruster T1 will continue to operate during the fault condition using power supplied from the second AC bus 2b through the active rectifier/inverter assembly 104d, the second DC interface assembly 22b, and the DC bus 34 of the power converter assembly 100 d. The propulsion motors connected to the non-faulted AC bus may also continue to operate normally.

If additional bow thrusters (not shown) are connected to each of the first AC busbar and the second AC busbar, for example by engaging AFE converters, the marine vessel may comply with the DYNPOS-AUTR requirements. For example, if there is a fault on the second AC bus 2b, the marine vessel will have one operable propulsion motor (i.e., the first propulsion motor PM1) at the stern as well as two operable bow thrusters, the bow thruster T1 that is to receive power from the first AC bus and a further bow thruster (not shown) connected to the first AC bus.

Claims

1. A power distribution system, the power distribution system comprising:

a first AC bus (2 a);

a second AC bus (2 b);

a first active rectifier/inverter (12 a) electrically connected to the first AC bus, the first active rectifier/inverter (12 a) having a first DC output terminal;

a second active rectifier/inverter (12 b) electrically connected to the second AC bus, the second active rectifier/inverter (12 b) having a second DC output terminal;

a first DC interface (22 a) connected to the first DC output terminal by a first DC link (14 a), the first DC interface (22 a) comprising a first reverse blocking device and a third DC output terminal;

a second DC interface (22 b) connected to the second DC output terminal by a second DC link (14 b), the second DC interface (22 b) comprising a second reverse blocking device and a fourth DC output terminal;

a third active rectifier/inverter (38) electrically connected in parallel to the third and fourth DC output terminals by a third DC link, the third active rectifier/inverter (38) having a first AC output terminal; and

a motor (T1), the motor (T1) being electrically connected to the first AC output terminal of the third active rectifier/inverter (38).

2. The power distribution system of claim 1, wherein each of the first and second reverse blocking devices comprises a string of one or more series-connected power semiconductor devices that provide a reverse blocking action.

3. The power distribution system of claim 1 or claim 2, wherein one or both of the first DC interface (22 a) and the second DC interface (22 b) further comprise one or more of:

DC fuses (24 a, 24 b),

circuit breakers (26 a, 26 b), and

common mode inductor filters (28 a, 28 b).

4. The power distribution system of claim 1, further comprising:

a second electric motor (PM 1), the second electric motor (PM 1) being electrically connected to the first AC bus (2 a) through a first power converter (100 c), the first power converter (100 c) comprising: the first active rectifier/inverter (12 a; 106 c) and a fourth active rectifier/inverter (112c);

the fourth active rectifier/inverter (112c) is electrically connected to the first active rectifier/inverter (12 a; 106 c) through the first DC link (14 a; 108 c) in parallel with the first DC interface (22 a) and to the second electric motor (PM 1) through second AC output terminals.

5. The power distribution system of claim 4, wherein the second electric motor (PM 1) is electrically connected to the first AC bus (2 a) through one or more further power converters (100 a, 100 b) in parallel with the first power converter (100 c).

6. The power distribution system of claim 4 or claim 5, further comprising a contactor (116) between the first power converter (100 c) and the second electric motor (PM 1).

7. The power distribution system of claim 4, further comprising:

a third electric motor (PM 2), the third electric motor (PM 2) being electrically connected to the second AC bus (2 b) through a second power converter (100 d), the second power converter (100 d) including:

the second active rectifier/inverter (12 b; 106 d), and a fifth active rectifier/inverter (112 d);

the fifth active rectifier/inverter (112d) is electrically connected to the second active rectifier/inverter (12 b; 106 d) through the second DC link (14 b; 108 d) in parallel with the second DC interface (22 b) and to the third electric motor (PM 2) through a third AC output terminal.

8. The power distribution system of claim 7, wherein the third electric motor (PM 2) is electrically connected to the second AC bus (2 b) through one or more further power converters (100 e, 100 f) in parallel with the second power converter (100 d).

9. The power distribution system of claim 7 or claim 8, further comprising a contactor (118) between the second power converter (100 d) and the third electric motor (PM 2).

10. The power distribution system of claim 1, further comprising a bus tie (6) for selectively connecting the first AC bus (2 a) and the second AC bus (2 b).

11. The power distribution system of claim 1, further comprising at least one AC generator (G1) electrically connected to the first AC bus (2 a) and at least one AC generator (G2) electrically connected to the second AC bus (2 b).

12. The power distribution system of claim 1, which is a marine power distribution and propulsion system.

13. A method of operating a power distribution system, the power distribution system comprising:

a first AC bus (2 a);

a second AC bus (2 b);

a first active rectifier/inverter (12 a) electrically connected to the first AC bus, the first active rectifier/inverter (12 a) having: a first DC output terminal;

a second active rectifier/inverter (12 b) electrically connected to the second AC bus, the second active rectifier/inverter (12 b) having: a second DC output terminal;

a motor (T1), the motor (T1) being electrically connected to the first AC output terminal of the third active rectifier/inverter (38);

the method comprises the step of operating the power distribution system in one of the following modes:

a normal or no-fault mode in which power is supplied to the electric motor (T1) from both the first and second AC buses (2 a, 2 b) through the first and second DC interfaces (22 a, 22 b) and the third active rectifier/inverter (36); and

a fault mode in which power is supplied to the electric motor (T1) from only one of the first and second AC buses (2 a, 2 b) through the respective first and second DC interfaces (22 a, 22 b) and the third active rectifier/inverter (36).

14. The method of claim 13, wherein the power distribution system further comprises:

a second electric motor (PM 1), the second electric motor (PM 1) being electrically connected to the first AC bus (2 a) through a first power converter (100 c) and through one or more further power converters (100 a, 100 b) in parallel with the first power converter (100 c), the first power converter (100 c) comprising:

the first active rectifier/inverter (12 a; 106 c), and

a fourth active rectifier/inverter (112c) electrically connected to the first active rectifier/inverter (12 a; 106 c) through the first DC link (14 a; 108 c) in parallel with the first DC interface (22 a) and to the second electric motor (PM 1) through second AC output terminals;

a first normal or no-fault mode in which power is not supplied to the electric motor (T1), and in which power is supplied from the first AC bus (2 a) to the second electric motor (PM 1) through the first power converter (100 c) and the one or more further power converters (100 a, 100 b);

a second normal or no-fault mode, wherein power is supplied to the electric motor (T1) from both the first and second AC buses (2 a, 2 b) through the first and second DC interfaces (22 a, 22 b) and the third active rectifier/inverter (36), and wherein power is supplied to the second electric motor (PM 1) from the first AC bus (2 a) through the one or more further power converters (100 a, 100 b); and

15. The method of claim 14, wherein the power distribution system further comprises:

said second active rectifier/inverter (12 b; 106 d), and

a fifth active rectifier/inverter (112d) electrically connected to the second active rectifier/inverter (12 b; 106 d) through the second DC link (14 b; 108 d) in parallel with the second DC interface (22 b) and to the third electric motor (PM 2) through a third AC output terminal;

a first normal or no-fault mode, wherein no power is supplied to the electric motor (T1), and wherein power is supplied to the second electric motor (PM 1) from the first AC bus (2 a) through the first power converter (100 c) and the one or more further power converters (100 a, 100 b), and/or power is supplied to the third electric motor (PM 2) from the second AC bus (2 b) through the second power converter (100 d) and the one or more further power converters (100 e, 100 f);

a second normal or no-fault mode, wherein power is supplied to the electric motor (T1) from both the first and second AC buses (2 a, 2 b) through the first and second DC interfaces (22 a, 22 b) and the third active rectifier/inverter (36), and wherein power is supplied to the second electric motor (PM 1) from the first AC bus (2 a) through the one or more further power converters (100 a, 100 b) and/or power is supplied to the third electric motor (PM 2) from the second AC bus (2 b) through the one or more further power converters (100 d, 100 e); and

16. The method of claim 15, wherein during a fault mode, electrical power is supplied to any one of the second electric motor (PM 1) and the third electric motor (PM 2), wherein the second electric motor (PM 1) or the third electric motor (PM 2) being supplied with electrical power is satisfied by the one or more further power converters being electrically connected to only one of the first and second AC buses.